1. Field of the Invention
The present invention relates in general to a data processing apparatus such as a word processor and an electronic typewriter, and more particularly to a program processing system for dealing with control programs for performing various data processing functions.
2. Discussion of the Prior Art
A known word processor, electronic typewriter or similar data processing apparatus can be temporarily loaded with optional or auxiliary programs for optional or special functions such as a word search or spell checking of entered text data, which are not offered by a standard control program provided as a standard or basic feature of the apparatus. These optionally provided programs are implemented, independently of the standard control program which is adapted to perform various basic data processing functions.
Described more specifically, when it is desired to perform an optional or special function during a data entry or processing operation, the control flow of the standard control program is once terminated, and then a suitable storage medium such as a PC board, module package or floppy disk storing an optional program is set in a data loading device provided on the apparatus, so that the optional program is executed such that the control flow of the optional program is independent of the control flow of the standard control program. After an operation to effect the relevant optional function according to the optional program is completed, the control should be restored to the standard control program to continue the data entry or processing operation.
Thus, the known program processing system deals with the optional programs independently of the main control program. In other words, the system and the standard program are not adapted to accept the optional programs so that the optional programs may be executed as if the optional programs were part of the standard program or as if they were originally provided on the apparatus.